1. Field of the Invention
The present invention relates to a method and apparatus for reducing exhaust gases, including hydrocarbons, in an initial cold start period, and, more particularly, to a method and apparatus for reducing exhaust gases, such as hydrocarbons, generated during an automobile low-temperature start.
2. Description of the Related Art
A catalyst device for reducing automobile exhaust gases including carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx), which are principal causes of air pollution, is widely used. However, most of the exhaust gases discharged from automobiles are generated in a period of heating a catalyst, that is, a period (cold start period or low-temperature start period) continuing until the temperature of a catalyst reaches an operation temperature (about 300° C.˜450° C.), at which a catalyst exhibits optimal catalytic conversion efficiency. Since the cold start spans a time period ranging from several tens of seconds to several minutes, various attempts to minimize exhaust gases during the low-temperature start period have been made. For reference, the “light-off temperature” in a catalyst is defined as the temperature at the point at which catalytic conversion efficiency surpasses 50%. Only when the temperature of the catalyst reaches the light-off temperature, the catalyst oxidizes both carbon monoxide (CO) and hydrocarbons (HC) and reduces nitrogen oxides (NOx), thereby converting them into harmless gases.
Accordingly, a method of mounting an electric heater or a burner on a catalyst device, that is, a catalyst preheating method, or a method of using heat included in exhaust gases discharged from an engine by closely mounting a catalyst device to an engine, that is, a close mounting method, has been used in order to help a catalyst reach the light-off temperature. Further, a method of purifying hydrocarbons in which hydrocarbons (HC), which are discharged in large quantities from an engine and pass through a catalyst device, are adsorbed on a separate trap, and are then discharged from the trap after the temperature of a catalyst reaches the light-off temperature, that is, an HC trap method, has been developed.
However, the above methods have various problems. For example, the close mounting method has a problem in that, when an engine normally operates, the temperature of a catalyst in the catalyst device increases excessively, thereby decreasing the expected life span of a catalyst. The HC trap method has a problem in that durability is reduced. Further, the above methods have a problem in that a large amount of precious metals, used to decrease the light-off temperature of a catalyst, entails high processing costs.